Battery powered, self-contained, water resistant barrier light structures for marking the presence of a construction site or other potentially hazardous location along a roadway have become a standardized means for warning oncoming motorists of nighttime roadway dangers. Typically, a barrier light structure is supported on a so-called barrier, horse or like support, and has a lens that is pivotable relative to a base so that, when a barrier light structure is being positioned at a construction site by a road worker, its lens can be oriented (i.e., pivoted) relative to its base for optimized viewability by the drivers of oncoming vehicles.
In a barrier light structure, the relationship between the light source (or bulb) and the lens is preferably such that the lens functions to focus the light leaving the lens into a predetermined pattern.
The conventional light source heretofore employed in a barrier light structure has been a small incandescent light bulb of the conventional type having a filament that when actuated (i.e., excited by electrical energy from the battery means in the base) emits light generally uniformly in all directions. Such a light bulb has been particularly convenient for use in a barrier light structure because the bulb was stationarily positionable at the focal point of the lens. Hence, the lens could be pivoted about a vertical axis that passed through the focal point, and the light-emitted by the energized bulb after passing through the lens, would be focused into a predetermined pattern, as desired.
The construction industry seeks to minimize the cost of labor associated with barrier lights. To avoid the manual labor requirement to turn each individual barrier light employed at a construction site on in the evening and off the following morning, it has become conventional to incorporate a photocell-actuated switch means into a barrier light structure. Thus, a barrier light structure so equipped automatically turns itself either on or off in response to the ambient light level. Although the typical so-equipped barrier light is also provided with manually operable on/off switch means, this latter switch means is seldom if ever used, even when a barrier light is being stored between usages, to avoid labor costs. The life of a set of non-rechargeable batteries in a barrier light is somewhat variable, being dependent on such variables as, for example, (a) whether the light is set to operate continuously or intermittently (i.e., blinks), and (b) the ambient environmental conditions (length of night, temperature, etc.). However, in field practice, batteries in a conventional barrier light are seldom replaced, owing to labor costs. The duty life of a conventional barrier light is thus practically set by non-rechargeable battery life. For a conventional prior art barrier light with a 6 or 12 volt incandescent light bulb and with two series-connected, standard size, lantern, non-rechargeable batteries, the battery operating life in a conventional barrier light structure is currently believed to be about 500 hours under average field conditions which translates into roughly about four to six weeks of use (or duty) life for a conventional barrier light structure.
The art needs an improved barrier light structure which is characterized by a substantially improved useful operating life preferably achieved from the same batteries as previously employed in prior art barrier light structures. The present invention satisfies this need by solving the below-characterized deviation angle problem:
Recently, new and very efficient light sources having limited light-emitting fields, such as light emitting diodes (LEDs), have become commercially available which typically have relatively broad spectral wavelength bandwidths and which exhibit efficient a high efficiency of conversion of electrical energy into photon energy (that is, a greater conversion efficiency than the conversion efficiency achieved by correspondingly sized conventional incandescent bulbs). Particularly because of their energy converting and using efficiency, such limited field light sources would appear to be attractive substitutes for conventional incandescent light bulbs in a barrier light structure. For example, a LED with a limited light emitting angle of about 34.degree. apparently can be continuously operated with a pair of series-connected, standard-size lantern, non-rechargeable batteries for a time of about 1,100 continuous hours. Theoretically, the duty life of a barrier light structure equipped therewith would be extended for a time that is at least about twice that of a corresponding prior art barrier light structure incorporating a uniformly light emitting prior art incandescent light bulb. A barrier light structure so equipped would have a useful operating life of roughly at least about three months using a single set of series-connected, standard-size, barrier, non-rechargeable batteries.
Compared to conventional incandescent light bulbs, however, such an LED suffers from a severe disadvantage: The light-emitted therefrom is distributed generally uniformly only in a limited field that extends only over a limited generally uniform angle that extends outwardly and laterally about a light emission center line that extends forwardly from the light emission point. For example, an LED 121 having limited light emitting angle 122 of about 34.degree. (or an angle 123 of about 17.degree. around and outwardly extending relative to the LED emission center line 124) is illustratively shown in FIG. 1.
Were such an LED 121 to be located in a fixed position at the focal point 125 of a barrier light structure lens 126, as shown, for example, in FIG. 2, so that the LED emission center line 124 is coincident with the lens axis or center line 127 that extends between the lens focal point 125 and the lens center point 128, substitution of such LED 121 for a conventional fixed position incandescent light bulb (not shown) would be possible, as those skilled in the art will readily appreciate. As used herein, the term "focal point" in reference to a barrier light structure lens 126 has conventional reference to the point from which light rays that diverge from a substantially point source along the lens 126 axis or center line 127 and that strike the inside face of the lens 126 are focused (or bent) by passage through the lens 126 to produce transmitted light rays that are substantially parallel to the lens center line 127.
In the art of barrier lights, it is preferred to employ as a lens 126 one which has a relatively short focal length. The term "focal length" as used herein in reference to a barrier light structure lens 126 has conventional reference to the distance from the focal point of a lens 126 preferably taken along the lens center line 127 to the lens 126 center point 128. In order to minimize the focal length in a barrier light lens, it is preferred in the art to employ a Fresnel lens which is a relatively thin lens constructed with stepped setbacks so as to have the optical properties of a much thicker lens.
However, when, as shown, for example, in FIG. 3, the lens center line 127 spatial position is changed while the spatial position of the LED 121 and also of the LED emission center line 124 remain fixed (as in a prior art barrier light assembly with a pivotable lens that is hypothetically fitted with an LED in place of the incandescent bulb), a severe problem arises. As the lens 126 is pivoted about a vertical axis 129 (indicated as a point in FIG. 3) that passes through the lens focal point 125 (and through the light emitting source in LED 121), emitted light from the LED 121 becomes increasingly lost and is not passed through the lens 126. The amount of light energy so lost is directly related to the size of the pivot deviation angle 131 that is defined between the lens center line 127 and the LED emission center line 124 relative to the lens focal point 125 taken as the apex of the deviation angle 131.
As the deviation angle 131 increases from the 0.degree. position shown in FIG. 2, the limited field light from the LED 121 that reaches and passes through the lens 126 decreases and becomes distorted. When the deviation angle 131 exceeds a maximum value, substantially no emitted light from the LED 121 is transmitted through the lens 126.
As a consequence of such light distortion and light energy loss, it is not possible merely to substitute a fixed position LED for a fixed position incandescent bulb in a prior art barrier light structure wherein the lens is so pivotable.
No way is believed to be known to the prior art by which this deviation angle problem could be overcome so that the LED could be used as the light source in a barrier light structure with a pivotable lens arrangement.
The present invention solves this deviation angle problem and enables one to use, in a barrier light structure having a pivotable lens, a limited field light source (such as, for example, an LED or the like, whose light-emitting field extends illustratively over a total included angle of not more than about 34.degree.). The duty life of the resulting barrier light structure is thereby greatly extended over the corresponding prior art barrier light structures, as desired.